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Abstract

Phenological synchrony of a consumer population
with its resource populations is expected to affect
interaction intensity. We quantified phenological variation
and synchrony of populations of an invasive Eurasian
flower head weevil, Rhinocyllus conicus, that consumes
florets, ovules, and seeds of developing flower heads of a
native North American thistle, Cirsium canescens, in Sand
Hills prairie in Nebraska, USA. Variation in timing of
adult activity among weevil populations was larger than
variation in timing of flower head development among C.
canescens populations, and it drove the observed variation
in the phenological synchrony between weevil and host
plant populations. Furthermore, the degree of phenological
synchrony between populations was significant in explaining
variation in weevil egg load on the newly
acquired host plant. Because population growth of C.
canescens is limited by predispersal seed losses to floral
herbivores, variation in the synchrony of herbivore and
plant flowering will affect the density of the plant
population. These results provide strong quantitative
support for the hypothesis that the synchrony of insect
activity with plant resources can determine the magnitude
of impact of floral herbivores on their host plant
populations.

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This is the authors' version of the work. It is posted here by permission of the publisher for personal use, not for redistribution.
The definitive version was published in Oecologia (2004) 139: 525–534; http://www.springerlink.com/content/6f69rcn2uxcrrmnu/